I still don't completely understand the difference between the Se and Si function, or at least I don't understand it on a sort of instinctive level. But I have been observing things and I have read about it, so this is sort of consolidation of my current knowledge, as much as I will be able to remember in the span of writing this blog.
There are a couple of difference between Si and Se. I am more of a Si user (my third function) and that means that I can at least recognize it in myself. I usually don't use Si be itself, but a lot of time it provides the input to my Ne function. In these cases I experience it as ideas, that I could connect with the certain memory. Maybe I remember hearing relevant stuff at the lecture, or maybe I remember how things were done somewhere else. A lot of my ideas were simply transporting a concept that I have noticed previously in the new situation.
On the other hand, Se was supposed to be experiencing the current situation with the five sense. I can try and contrast this with the Ti function. When there was a car crash one, I remember going from one point to another. Alright, she is laying there. I need to get he away from the street. Is there a car there? No, I can go there,... But an ESTP that I know says that when something like that happens, you simply act and there is no verbal argumentation and thinking what is should be done involved. You just react. Somehow. Don't ask me how this is possible, because I have no idea, but that is what she had told me. But it does sound a lot different than what I described above.
There are also a couple of differences that I have discovered with my theoretical research. One of them is the time. Si-types are much more likely to be thinking about the past, and the Se-types are much more likely to be thinking about the present. Based on this time dimension, the Si-types are much more likely to enjoy the status quo, while the Se types are much more likely to try something new and not be that possessive of the current status quo.
The second difference that my theoretical research uncovered was the difference between sensory experience and minimalism. The Si-types are much more likely to be minimalistic and have a bland tastes. So they are alright to eat the same food everyday (at least based on the experience in my family), they are more likely to live in a sort of minimalism and they are more likely to not care about the material possessions that much. They are also more likely to be alright with what they have.
The Se-types, on the other hand, are much more likely to appreciate the sensory experiences. The good food, the new adventure, the travels, the material wealth and so on. That is why they are much more likely to be quite excessive in this, like buying a good car or television on a whim or going out to eat or spending a lot of time preparing good meals and so on.
And this is my current knowledge, but I will certainly be building on it as I go along.